area magnetic
unreliability. In
the polar region,
magnetic
heading is
unreliable or
totally useless
for navigation.
Magnetic
variations
typically are
extreme, often
are not constant
at the same
point, and
change rapidly
as an airplane
changes
position. Flight
crews must
ensure that the
computer flight
plan shows
true tracks and
headings. It is
important to
note that areas
unmapped
for enhanced
ground
proximity
warnings
systems (i.e.,
those areas
beyond the
limits of
the terrain
database) are
displayed as
magenta dots on
the map display,
regardless
of airplane
altitude. The
Canadian area
of magnetic
unreliability
encompasses
the NCA and the
Arctic Control
Area. The
Russian area
of magnetic
unreliability is
not formally
defined.
Russian airways
south of 74
degree north
latitude are
referenced to
magnetic north.
Flight crews
should use
caution when
using automatic
direction finders
(ADF) or VHF
Omni range
navigation
equipment
(VOR), or
both, because
the heading
reference in
use will affect
the display
of data. With
the heading
reference in
TRUE, ADF
bearings are
true and vice
versa. VOR
radials are
displayed
according to the
orientation of
the VOR station,
either true
or magnetic.
Crews should
be prepared
to operate in
QFE and metric
altitude where
required. Some
airports will
provide QNH
upon request
even if their
standard is QFE.
F
or all polar
operations,
operators
will have the
minimum flight
equipment. For
multi-engine
aircraft shall
have an APU
that includes
pneumatic/
electrical
operation.
Flight crew
communication
system that
meets the
standards of
the FAA. Fuel
quantity system
that indicates
fuel temp.
Because of the
extended flight
duration and
the prevalence
of very cold air
masses on the
polar routes,
the potential
exists for fuel
temperatures
to approach
the freezing
point. However,
current airplane
systems and
operating
procedures
provide
confidence
that fuel will
continue to flow
unobstructed
to the engines
in all plausible
cold-weather
conditions
likely to be
experienced on
polar routes.
The Jet A fuel
specification
limits the
freezing point
to a maximum
of –40°C; the
Jet A-1 limit is
–47°C maximum.
In Russia, the
fuels are TS-1
and RT, which
have a maximum
freezing point of
–50°C. However,
the fuel freezing
point is not
what dictates
fuel flow to the
boost pumps.
The critical
condition of
cold fuel in an
airplane fuel
tank, in terms of
flight safety, is
its propensity to
flow toward and
into the boost
pump inlets.
Pumpability,
or flowability,
depends on the
pour point of
the fuel, defined
as the lowest
temperature at
which the fuel
still flows before
setting up into a
semirigid state.
Generally, the
pour point is
approximately
6°C lower than
the fuel freezing
point. However,
the exact
relationship
between
freezing point
and pour point
depends on the
source of the
crude oil and
the refining
processes.
Because jet fuel
is a mixture of
many different
hydrocarbon
molecules, each
with its own
freezing point,
jet fuel does
not become
solid at one
temperature as
water does. As
fuel is cooled,
the hydrocarbon
components
with the highest
freezing points
solidify first,
forming wax
crystals. Further
cooling causes
hydrocarbons
with lower
freezing points
to solidify.
Thus, as the
fuel cools, it
changes from
a homogenous
liquid to a liquid
containing a few
hydrocarbon
(wax) crystals,
to a slush
of fuel and
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